Injection molding techniques have for some time been used for molding various parts, particularly of plastic. The injection molding apparatus conventionally consists of a mold formed of two halves typically, one or more pairs of fixed and movable bases (also referred to A and B mold bases respectively), which are mounted, respectively, on the top clamp plate and base support plate of the injection mold base mounted on the molding machine. Mold inserts, plural A and B mold inserts, which are adapted to fit into the fixed and movable sides of the machine usually have mold cavity defining means which are fixed in the bases in paired alignment, whereby upon closure of the base support plate toward the top clamp plate respective pairs of oppositely disposed mold inserts are brought together to close the mold cavities. Molding material is fed through the top clamp plate and A mold base thereon to a runner distribution system in the two mold sides, and molding material is delivered from such distribution system to respective mold cavities to mold parts. An ejector apparatus usually is provided to eject the molded parts from the opened mold cavities and the excess mold or runner from the runner distribution system by means of ejector pins that extend, for example, through the base support plate, B mold base and B mold inserts mounted thereon.
Moreover, molds with removable mold inserts for mold frames are in use and are especially valuable for prototype or low production molding needs wherein the tooling is changed after relatively short time. However, the known molds of this type only allow for molding of several like-parts and do not allow for the molding of different parts. In order to mold a different part, the entire mold assembly must be changed. Because only the same mold inserts can be used at the same time, the molding of different parts still requires substantial changeover time. The need exists for an inexpensive and efficient mold injection apparatus, which molds different parts at the same time and requires only minimal changeover time and machining operations.
Another concern in the injection molding industry is the method of gating into a part. Weld lines are places where multiple flow fronts in injection molding meet. These regions are not usually as strong as the rest of the part. Since they can introduce weakness into the part, reducing weld lines in injection molding remains a primary concern. The following methods exist to minimize the effect of weld lines: (1) locate weld lines closer to a gate to make them strong; (2) provide venting at the weld line; (3) increase part thickness at the weld line; (4) increase melt temperature; and (5) increase injection pressure and speed.
In addition to the foregoing, center gating, which is used to mold round or cylindrical parts, reduces the well lines formed when molding a circular part rather than edge gating or gating through the main parting line of a mold assembly. The uniform flow of an injection molding material from the center of a round part radially outwards produces a stronger part, as the molding material is uniformly molded from the center and then radially outwards. Because geometry of a desired part dictates how it should be gated, circular parts that require the ability to withstand an equal stress distribution around the center of the circular part are best molded if the molding material enters through to the center of the part, and molds radially outwards from the center of the part. This is accomplished by center gating directly into a mold insert. The need also exists for a mold injection apparatus with removable mold inserts, which allow center gating directly into the mold insert.
Previous attempts to provide an injection molding apparatus containing removably interchangeable molding tools or removable and interchangeable mold inserts are described in U.S. Pat. No. 3,871,611 to Taketa ('611 patent); U.S. Pat. No. 4,828,479 to Pleasant ('479 patent); and U.S. Pat. No. 4,959,002 to Pleasant ('022 patent); all of which are incorporated herein by reference. In addition, previous attempts to provide different gating techniques are described in U.S. Pat. No. 5,798,069 to Bertschi et al. ('069 patent) and 5,324,191 to Schmidt ('191 patent), both of which are also incorporated herein by reference.
The '611 patent describes an improved mold having removable and replaceable cores (mold inserts or molding tools) and cavities, so that the need of providing a new mold base for every new part or product is eliminated. The arrangement of the mold is such that the cores and cavities can be easily and quickly removed and replaced with minimum down time of the molding apparatus.
The '479 patent describes a molding apparatus for use with removable inserts, described in patent '002. The molding apparatus comprises a cavity insert for the injection side and a core insert for the ejection side of a mold which are each shaped as a generally cylindrical, stepped body provided with circumferentially extending locking grooves and a liquid cooling or heating channel. Insert retainers and lifters having rotatable elements with locking tongues engaging the locking grooves clamp the inserts in the main mold frame. The main mold frame is provided with liquid conduits opening to opposite ends of the liquid channels so that the need for machine liquid conduits and channels for different inserts is avoided. Ejector tooling may be connected to the core insert for insertion and removal with it.
The '069 patent describes an opposed gating injection method and apparatus for forming molded articles from a composite of materials with injection molders having a first mold half and a second mold half adapted to cooperate to form at least one mold cavity. A first injection means is positioned in the first mold half adjacent the one cavity for injecting a first molding resin onto the mold cavity through a first orifice. A second injection means is included which is positioned in the second mold half adjacent the mold cavity for injecting a second molding resin.
The '191 patent describes an improved sealed edge gate arrangement for use in an injection molding machine which comprises a nozzle assembly having a tip end and at least one melt channel extending into the tip end and an annular seal or sealing ring snuggly fit over the tip end of the nozzle assembly. The seal ring has at least one melt channel for mating with the at least one melt channel in the nozzle assembly.
None of the devices mentioned above comprise an injection molding apparatus which simultaneously molds different components while allowing the easy replacement of each different mold insert. The '611 patent describes removable mold inserts and a mold assembly which only allows for the simultaneous molding of like components. Similarly, the '479 patent describes a molding apparatus which allows for removable inserts but does not allow for the simultaneous molding of different components.
Moreover, none of the devices mentioned above employ a removable mold insert, which allows gating directly into the mold insert, in conjunction with the simultaneous molding of a plurality of different parts. Both the '069 and '191 patent provide an improved apparatus for the use of improved gating methods but neither patent provides for an injection molding apparatus with removable mold inserts or molding tools which can simultaneously mold a plurality of different parts and which removable inserts provide for center gating.
The above inventions only allow for the use of a uniform set of removable mold inserts. Variation of the parts to be molded requires changing the entire mold assembly. Simultaneous molding of different components can only be achieved by using two separate molding apparatuses, one mold assembly containing a particular uniform set of mold inserts and another mold assembly containing another particular set of uniform of mold inserts.
Consequently, there is a need in the art for a molding press injection apparatus with removable inserts or molding tools, that allows the simultaneous molding of different parts.
There is a further need in the art for an injection molding apparatus, which quickly molds the different parts.
Finally, there is a further need in the art for a molding press injection apparatus with removable inserts which provides center gating directly into each removable mold insert.